; Parse ASCIIZ string into FCB
; IN	SI	ptr to filename
;       BX	ptr to FCB
fcb_parse:
  push di
  push ax
  mov di, bx
  xor ax, ax
  stosb
.cleanout:
  push di
  mov cx, 0x0A
  mov al, 0x20
  rep stosb
  pop di
.base_loop:
  call .read
  cmp al, 0x2E
  je .ext_start
  cmp al, 0x20
  je .ret
  stosb
  jmp .base_loop
.ext_start:
  mov di, bx
  add di, 9
.ext_loop:
  call .read
  cmp al, 0x20
  je .ret
  stosb
  jmp .ext_loop
.read:
  lodsb
  test al, al
  jz .eret
  cmp al, 0x0D
  je .eret
  ret
.eret:
  dec si
  pop ax
.ret:
  pop ax
  pop di
  ret

fcb_open:
  cmp byte [bx], 0
  jne .drivedone
  mov al, default_drive
  inc al
  mov [bx], al
.drivedone:
  push bp
  sub sp, bpb_size
  mov bp, sp

  mov dl, [bx]
  dec dl

  call bpb_load
  mov ax, [bp]
  mov cx, [bp+2]
  mov dx, [bp+4]
  mov bx, [bp+6]

  add sp, bpb_size
  pop bp
  ret